A voltage regulator is often employed to supply a stable, regulated, voltage having a predetermined voltage level to one or more circuits in an electronic device.
When a voltage regulator is included in a battery-powered device, such a mobile phone (e.g., a smartphone), a few performance parameters become particularly important.
One of these parameters is the drop out voltage of the voltage regulator, which is the difference between the minimum supply voltage which supplies the regulator and the regulated voltage output by the voltage regulator. In many cases it is desired for a voltage regulator to have as low of a drop out voltage as possible, especially in the case of battery-operated devices (e.g., mobile phones) where the battery voltage level is generally relatively low to begin with, and which may drop significantly as it is drained to a specified minimum battery voltage level at which the battery-operated device is expected to still operate properly.
Another important parameter for a voltage regulator is power consumption, that is, the power which is consumed by the voltage regulator itself separate from the power consumed by any load which is supplied by the voltage regulator. Power consumption may be related to the efficiency of the voltage regulator which maybe expressed in terms of the current or power which the voltage regulator supplies to a load compared to the power consumed by, or the quiescent current of, the voltage regulator itself. In many cases it is desired for the voltage regulator to be as efficient as possible, or to have as low of a power consumption as possible given the required load current, especially in the case of battery-operated devices (e.g., mobile phones) where the battery, where there may be a total power budget for the device in which case energy which is consumed by the voltage regulator drains the battery and reduces the time between battery recharges or replacement (for devices with non-rechargeable batteries). Low power consumption by a voltage regulator may be particularly important in the case of a battery-operated device, since the voltage regulator may, in general, always be operating or “on” as long as the device itself is operating.
Yet another important parameter for many voltage regulators is phase margin or stability. More specifically, some voltage regulator circuits employ feedback to maintain the regulated voltage level within a specified range or tolerance. In that case, if the phase margin of the feedback loop is too low, then the voltage regulator may begin to oscillate. This may occur, for example, if the quiescent current of the voltage regulator is too small, particularly at low load currents. The quiescent current of the voltage regulator may be increased to increase the phase margin, but that will increase the power consumed by the voltage regulator and decrease its efficiency, which as explained above is undesirable.
What is needed, therefore, is a voltage regulator which can simultaneously provide a low dropout voltage and adequate phase margin, while not consuming an unnecessarily large amount of power.